Student Belt Recipe = Almost infinite Crystals

[Loopy]

Every level 4 recipe costs runes to craft, but they do in fact have the possibility to yield 2 runes when you salvage them. All level 4 recipes costs 16 crystals, 16k gold, 80 mana, and 1 rune, with the exception of Splinter of Darkness which costs one of each rune. So it is theoretically possible to generate infinite runes.